The present invention relates to enabling an operator to drill holes and optionally insert fasteners, and, in particular to drilling holes and optionally inserting fasteners through multi-layer structures by utilizing an electromagnet assembly to securely clamp the multi-layer structure together during the operation.
The fasteners that hold together multi-layer structures, particularly those structures that are subject to significant dynamic forces and/or pressure over their lifetime, such as aircraft bodies, bridges, vehicle bodies, buildings, and others, must be properly secured in order to ensure that the structure will perform as intended over its lifetime. In order to properly secure a fastener in a multi-layer structure, the fastener hole must not have any sharp edges, i.e., burrs, there must not be debris between the layers, and any sealant applied between the layers in order to make the structure air and/or water tight must be sufficiently squeezed out. When excess sealant is present between the layers, the distance between the layers is increased and/or uneven, which may be referred to as a “gasket” condition. Thus, if burrs, debris and/or excessive sealant are present, then the layers cannot be properly fastened and the layers may suffer corrosion, cracking and/or premature fatigue failure, which generally renders the structure ineffective for its intended purpose and, therefore, subject to the expense of repair or replacement.
Thus, ensuring that a burr-less hole is drilled, that there is no debris between the layers, and that sealant is properly applied between the layers is an integral part of fastening multi-layer structures together. In the aerospace industry, for example, a significant amount of time and labor is expended ensuring that the holes through the various layers of the aircraft structure are appropriately drilled, cleaned, sealed and fastened. Initially, the layers of materials that form the structure are loosely assembled without sealant, and drill templates are aligned and attached to the structure in the areas to be drilled. A drill operator, guided by the drill template, then drills holes through the layers of materials typically using a manual drill motor. As the hole is being drilled through the layers, the drill bit tip pushes with the full feed force applied to the drill motor. This can cause a gap to develop between a drilled layer and the next layer, particularly when the layers are a stack up of thin material. The gap between the layers causes burrs about the hole and debris is likely to gather between the layers. Thus, once the holes are drilled, the layers must be disassembled, the burrs must be removed from the holes, and the debris must be cleaned from the surfaces of the layers, all of which is a time-consuming and labor intensive process.
Sealant is then applied to the layers prior to re-assembling the layers. In order to ensure the layers are properly sealed to provide an air and water-tight seal, a generous amount of sealant is applied to the layers. Clamps that extend through the holes, such as KWIK-LOK™ clamps commercially available from Zephyr Manufacturing Company, Inglewood, Calif., must be placed through each hole of the reassembled layers in order to squeeze out the sealant to prevent excessive “gasket” between the layers before the sealant dries. The extra sealant squeezes out around the clamps and must be cleaned from the structure and the clamps during clamping and/or after the clamps are removed.
Once the sealant is cured, the clamps may be removed and the holes may be countersunk. In order to countersink a hole, a countersink drill bit and microstop countersink cage are attached to the drill motor and the operator revisits each hole to drill the countersink. The holes are then inspected to ensure they were properly countersunk. The holes may be inspected by checking the countersink of each hole with a measuring tool, or by installing the fastener to check if it fits properly within the hole and countersink. If the holes are satisfactory, then fasteners may be installed and fastened with nuts or swage lock collars. Overall, this process is expensive, laborious, and time-consuming. In addition, the integrity of the resulting holes depends upon the completion of many manual processes, which creates a risk that certain steps may be performed inadequately or completely overlooked.
Therefore, a need exists to drill holes and install fasteners in multi-layer structures in a more efficient manner, such as by reducing or eliminating the time and expense involved in disassembling the drilled layers, de-burring the holes, cleaning the debris from the layers, reassembling the layers, clamping the holes, waiting for the sealant to dry, and revisiting the holes to drill the countersink. In particular, there is a need to efficiently drill holes and install fasteners in multi-layer structures in one operation, such that the time and money involved in the manufacture of multi-layer structures is significantly reduced.